An apparatus for producing a plate glass using a float method, is an apparatus for producing a band-shaped plate glass having a predetermined plate thickness, by supplying a molten glass on a molten tin (molten metal) reserved in a bath to form a molten glass ribbon, and pulling the molten glass ribbon towards a layer (gradual cooling apparatus) disposed continuously from an exit of the bath.
Heretofore, in the production of plate glass using the float method, an upper space above the bath surface is filled with a reducing gas (reducing property is obtained mainly by hydrogen gas and nitrogen gas) to prevent oxidation, since oxide of molten tin tends to adhere to a back surface of a plate glass or oxide or compound of tin evaporated from a bath surface of the molten tin tends to adhere to a front surface of the plate glass, or the adhered matter tends to form a defect of a product or causes to form a defect such as scratch at a time of conveying the plate glass. The gas is supplied to a ceiling portion of the bath by a reducing gas supply pipe, and the gas is further supplied to an upper space above the bath surface of the molten tin through a brick wall (roof brick) of the bath. The supplied gas is exhausted mainly through an exit of the bath or an exhaust port provided to exhaust a gas, to the outside of the bath.
However, there is a case where tin, tin oxide or tin compound evaporated from the bath surface of molten tin, adheres to the front surface of molten glass ribbon, and as a measure for this problem, Patent Document 1 proposes to provide a partition wall for partitioning an upper space above a bath surface of molten tin into an upper space above a region covered with the molten glass ribbon and an upper space not covered with the molten glass ribbon. Further, in order to prevent deterioration of heaters provided in the bath by a reducing gas, the document proposes to provide 100% nitrogen gas to the upper space above the region covered with the molten glass ribbon partitioned from the upper space by the partition wall, and proposes to supply a nitrogen gas containing 10% of hydrogen gas to the upper space above the region not covered with the molten glass ribbon.
Patent Document 1: JP-A-11-310421